1. Field of the Invention
The present invention relates in general to a safety device for an microwave oven and, more particularly, to a structural improvement in such a safety device for simplifying the structure of the microwave oven and reliably preventing possible damage of the microwave oven caused by overheat of either the magnetron or the heating cavity of the microwave oven.
2. Description of the Prior Art
Typical microwave oven may have danger of a fire in their cavities due to careless operation of the users or forcible operation under the abnormal conditions of the microwave ovens. When the microwave oven is carelessly operated with no food charged in the heating cavity of the microwave oven, the microwave emitted from the magnetron returns to the magnetron due to no food to be heated in the cavity. When the magnetron is overheated as described above, the magnetron will be overheated to be seriously damaged.
In an effort to combat the above problems of the typical microwave ovens, the microwave ovens are preferably provided with their safety devices. With reference to FIGS. 1A and 1B, there is shown an microwave oven with a typical safety device. As shown in these drawings, the microwave oven includes a heating cavity 100 which will be charged with food to be heated and cooked by the microwave energy. A magnetron 110 is mounted to a side of the cavity 100 and generates the microwave used for heating the food in the cavity 100. The microwave oven also includes an air exhaust port 120 which is formed in the top wall of the cavity 100 such that the port 120 is opposite to the magnetron 110. The port 120 is used for exhausting the air of the cavity 100 to the outside. An oven thermostat 130 is provided on the top wall of the cavity 100 about the exhaust port 120 and used for sensing the inner temperature of the cavity 100 by checking the air exhausted from the cavity 100 through the port 120. The thermostat 130 has a bimetal structure which will cut off the electric power for the microwave oven when the thermostat 130 senses that the inner temperature of the cavity 100 is abnormally increased. The microwave oven further includes a magnetron thermostat 140 which is provided about the magnetron 110 and used for cutting off the outside electric power for the magnetron 110 when the temperature of the magnetron 110 is higher than a predetermined allowable temperature. In the above drawings, the reference numeral 150 denotes a casing which surrounds and protects the parts of the microwave oven and the numeral 160 denotes an air suction port which is formed in the cavity wall and used for sucking the outside air into the cavity 100 therethrough.
Turning to FIG. 2, there is shown a circuit of the typical safety device provided in the microwave oven of FIG. 1A. The above safety device includes a power plug 200 and a fuse 210. The oven thermostat 130, which will cut off the electric power for the microwave oven when the temperature of the exhaust air discharged from the cavity 100 through the port 120 is higher than the allowable temperature, is included in the safety device. The safety device also includes the magnetron thermostat 140 which will cut off the outside electric power for the magnetron 110 when the temperature of the magnetron 110 is higher than the allowable temperature. The circuit of the safety device is controlled by a control unit 220. The device further includes a first switch 230, an oven lamp 240, a fan motor 250, a turntable motor 260, a second switch 270, a transformer 280, a high voltage capacitor 290 and the magnetron 110. The first switch 230 selectively opens the circuit to stop the magnetron 110 when the door of the microwave oven is opened. The oven lamp 240 lights the inside of the cavity 110. The fan motor 250 generates the rotational force for sucking and exhausting the air relative to the cavity 100, while the turntable motor 260 generates the rotational force for rotating a food turntable (not shown) in the cavity 100. The second switch 170 is a safety switch which will cut the fuse 210 and open the circuit when the first switch 230 is out of order. The transformer 180 converts the input voltage into a high voltage. The high voltage capacitor 190 doubles the high voltage of the transformer 280 prior to applying the voltage to the magnetron 110. The magnetron 110 is applied with the high voltage from both the transformer 280 and the high voltage capacitor 290 and generates the microwave for heating the food laid on the turntable in the cavity 100.
The control unit 220 in turn includes a first connector 221 for connecting the outside electric power to first and second internal relays 222 and 223. The first relay 222 selectively relays the outside electric power to a function control panel (not shown) of the microwave oven as desired. The second relay 223 relays the input power to all of the oven lamp 240, the fan motor 250 and the turntable motor 260. The control unit 220 also includes a third relay 224 which controls the operation of the magnetron 110 and in turn controls the output of the magnetron 110. The control unit 220 further includes a second connector 225 which connects the output electric power to a control switch 226. The control switch 226 is for controlling the operation of the relays 223 and 224.
In operation of the above electronic microwave oven, the range is applied with the outside electric power through the plug 200 and performs a cooking mode which is selected by the user by operating the function control panel (not shown). When the selected cooking mode is performed, the air sucked into the cavity 100 through the air suction port 160 as shown in FIG. 1B and heated in the cavity 100 by the microwave of the magnetron 110. The heated air is, thereafter, exhausted to the outside of the cavity 100 through the air exhaust port 120. In the case, when the temperature of the exhaust air discharged from the cavity 100 through the port 120 is higher than the allowable temperature, the oven thermostat 130 senses the overheated exhaust air temperature and cuts off the outside electric power for the microwave oven and thereby preventing possible overheat of the cavity 100.
When the microwave oven is carelessly operated with no food charged in the cavity 100, the microwave emitted from the magnetron 110 will return to the magnetron 110 and overheat the magnetron 110. In order to prevent such an overheat of the magnetron 110, the magnetron thermostat 140 is provided about the magnetron 110 and checks the peripheral temperature of the magnetron 110. In the same manner as described for the oven thermostat 130, the magnetron thermostat 140 cuts off the outside electric power for the magnetron 110 when the magnetron temperature is higher than the allowable temperature and thereby prevent possible overheat of the magnetron 110.
However, the above safety device for a microwave oven has a problem in that the safety device for a microwave oven has a complicated construction and increases the cost because the microwave oven device separately includes two thermostats 130 and 140, which are used for preventing possible overheat of the cavity 100 and possible overheat of the magnetron 110 respectively, even though the functions of the two thermostats 130 and 140 are practically same with each other.